IVL Swedish Environmental Research Institute

Stockholm’s Innovations in District Heating & Cooling

Central Stockholm is the location of one of Europe’s largest district heating and cooling systems. Close to 90% of Stockholm’s buildings are connected to the district heating network.

Stockholm Exergi is responsible for heating and cooling production in the region of Stockholm. The last coal-fired power plant in Stockholm closed down in April 2020 and now the district energy network is primarily based on renewable energy sources.

The district heat distribution network in Stockholm has a length of 3000 km. The heat supply system of Stockholm Exergi uses a variety of energy sources such as biofuel and waste from households and industries. The following innovative solutions render Stockholm’s heating and cooling network to have a low climate impact:

Seawater district cooling facility at Värtan Ropsten
The first heating plant was connected to the district heating network in Stockholm at Värtan in 1969. The district heating network has since then been expanded to include both heating and cooling, and is today one of the world’s largest sea water based facility. In the summer, the freezing cold water from the lake in Ropsten is primarily utilized for the cooling network. In the winter, heat pumps are used.

Excess Heat from Data Centres
Stockholm has established itself as a world leader in large-scale heat recovery from data centres. Excess heat from multiple data centres in Stockholm is utilized in the district heating network. In the future, Stockholm Exergi aims to provide 10 % of the city’s heating needs with recovered heat from data centres.

Heating and Cooling from Purified Wastewater at Hammarbyverket
Hammarbyverket is the world’s largest heat pump plant that extracts district heating and district cooling from purified wastewater. The plant consists of seven heat pumps with a total power of 225 MW, which is enough to heat 95,000 two-room apartments during a normal cold winter. Purified wastewater comes from Henriksdal’s wastewater treatment plant to the Hammarby plant heat pumps. The heat pumps utilize the energy contained in purified wastewater from Henriksdal’s water treatment plant. The heat produced is utilized in Stockholm’s district heating network. At the same time, the process generates cold water, which in the next step is used to produce district cooling to the city’s district cooling network.

Since the Hammarby plant came into operation in 1986, emissions of sulfur oxide and dust in the air over Södermalm have decreased by two-thirds, thanks in large part to the fact that many property owners have switched from individual heating to district heating.

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